It has long been desired to prepare compositions for roof membranes, roof flashing, and liners to contain liquids for such applications as pools and for holding waste liquids. Naturally, to be commercially acceptable, such compositions must be low in cost and have good physical properties. Because of the ready availability of asphalt and its comparatively inexpensive price, this material has found wide application in this area. Unfortunately, the physical properties of asphalt leave much to be desired. Conventional asphalt's resistance to oxidation and ultraviolet radiation and its tensile strength are not sufficient.
To overcome these problems, a minor amount of elastomeric materials has to be added to asphalt. For example, Boyer et al. in U.S. Pat. No. 4,371,641 shows the addition of from 5 to 25 wt. % of a neutralized sulfonated polymer to 100 parts of bitumen. The invention specifically teaches that it is preferred to use only about from 7 to about 20 parts of the polymer. The preferred embodiments, shown in the examples, all add 10 parts per hundred.
Physical properties of the above compositions are improved in contrast to the bitumen per se; however, in general, the properties of such compositions still fell far short of those desired for the rigorous environmental and/or structural conditions to which such compositions are exposed in that, in order to obtain satisfactory performance, thick sections often had to be utilized as well as reinforcing material.
Other references show the use of a broad range of polymeric material to modify the properties of asphalt compositions. For example, U.S. Pat. Nos. 4,328,147 and 4,382,989 to Chang et al. show the addition of 1 to 8 wt. % of an oxidized polyethylene to a roofing asphalt formulation. The purpose here is to affect the softening point, penetration and viscosity of blends. Such small amounts of polymer, however, would not be effective in increasing the tensile strength of the composition to that considered necessary for waterproof membrane applications.
Rollmann, in U.S. Pat. No. 4,460,723, shows the addition of various polymers to asphalt to broaden the useful temperature range of the asphalt composition by improving its ductility at low temperature and its resistance to flow at elevated temperatures. Many rubbery polymers are described, including polybutadene, polyisoprene, natural rubber, butadiene/styrene copolymers, ethylene/propylene/diene terpolymers, isobutylene/isoprene copolymers, and isoprene/styrene copolymers. The elastomer is present from about 1 to about 30 wt. %, preferably from 5 to 20 wt. %, based on the total asphalt composition. Because of the limited amount of the rubbery polymer used and the particular polymers selected, such compositions do not enjoy particularly high tensile strength and therefore they would not be suitable for numerous membrane applications.